Create Codesemble GitHub Pages landing page

[pate0304]

Outcome

Add a clear, interactive GitHub Pages landing page for Codesemble and link it from the README.

Changes

• Add a responsive static site under site/ with accessible team tabs, evidence chips, copyable install commands, expandable preview explanation, and semantic control-flow diagrams.
• Add a branded ImageGen prism visual plus an optimized project-local brand asset.
• Add a pinned GitHub Pages workflow for main and the focused branch.
• Add the Pages link to README.md and regenerate the README checksum.

Validation

• npm run check — 20 files, 140 tests
• repository, deterministic archive, SBOM, checksum, and dependency checks
• static asset, hash-link, external-link, HTML/JS syntax, YAML, and local HTTP smoke checks

Safety and privacy

Static documentation only. No plugin runtime, permissions, credentials, or global Codex configuration changes. Existing dirty branding assets remain outside the focused worktree.